In recent years greater demands have been made of display devices, including thinness, larger area and lower power consumption. In order to meet these demands, research is being done into the use of cold cathode electron sources, which have little heat loss at the electron source.
1991 saw the development of carbon nanotubes, a tubular carbon material with a diameter of tens of nm and a length of several μm. Before this development, many displays had been reported using so-called spint-type cold cathodes formed from metal in circular cone form (for example, Journal of Applied Physics Vol. 39, No. 7, p. 3504 (1968)). However, carbon nanotubes have not only the superior electrical conductivity, thermal conductivity and corrosion resistance of carbon material, but also an extremely small radius of curvature. Consequently, carbon nanotubes hold promise as highly efficient and sturdy emissive elements which are stable even in low vacuum. As a result, the main thrust of research and development has begun to turn towards carbon nanotubes (for example, Applied Physics Letters Vol. 78, No. 4, p. 539 (2001)).
In Japanese Unexamined Patent Publication No. 2000-178016 it is disclosed that an artificial graphite sheet can be obtained by two-stage baking of a polymer sheet. This graphite sheet has the high flexibility in addition to the superior electrical conductivity, thermal conductivity and corrosion resistance of the carbon material. And this graphite sheet is made from a polymer sheet. Accordingly, a sheet with a large area can be formed easily.